"The Broader and Wider Information Road" Information Transmission PPT Courseware

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"The Broader and Wider Information Road" Information Transmission PPT Courseware

1.Microwave communication

Read the textbook and answer the questions: (Compare to see who can find it faster)

1. Why use microwave communication?

2. What is the wavelength range and frequency range of microwaves?

3.What are the properties of microwaves?

4.What is the function of microwave relay station?

5. What are the distance requirements for establishing a microwave relay station?

6. Can the moon, the earth’s natural satellite, be used as a relay station?

1. Why use microwave communication?

Information theory shows that the higher the frequency of electromagnetic waves, the more information can be transmitted in the same time. Microwave has a higher frequency than medium wave and short wave, and can transmit more information within a certain period of time.

2. What is the wavelength range and frequency range of microwaves?

The wavelength of microwave is between 10m-1mm, and the frequency is between 30MHz-3×105MHz.

3.What are the properties of microwaves?

The properties of microwaves are closer to those of light waves: they propagate roughly in straight lines.

Advantages and disadvantages of microwave communication:

advantage:

Microwave communication has a high frequency and a large capacity for transmitting information, and the relay station is supervised and controlled by a computer. It can automatically switch and alarm when a fault occurs, saving human resources.

shortcoming:

The farther the microwave transmission distance is, the more relay stations need to be established, which will inevitably cause certain troubles. Moreover, when encountering snowy mountains and oceans, it is impossible to establish relay stations.

1. Microwave communication

1.Definition: wavelength is between ___________, frequency is between _______________

_______between.

2.Features

(1) A microwave line can open ______ and _______ circuits at the same time.

(2) Propagates roughly along _______ and cannot be diffracted along the earth's surface.

3. The role of a relay station: A microwave relay station should be built every _________ or so to process the signal from the previous station and then transmit it to the next station so that the signal can travel along the Earth_______.

2. Satellite communications

Using communication satellites for microwave communication ________, satellite communication can be realized. Global communication can be realized by arranging ___ synchronous communication satellites evenly around the earth.

Optical fiber communication technology has only been developed in recent decades

In 1966, the Chinese physicist Kao Kun first proposed the concept of low-loss (20 db/km) optical fiber (referred to as optical fiber) using the principle of radio waveguide communication.

In 1970, Corning Company of the United States successfully developed quartz optical fiber with a loss of 20 db/km for the first time, which is an ideal transmission medium.

In 1970, Bell Labs successfully developed a continuously oscillating semiconductor laser (LD) at room temperature. Since then, the era of rapid development of optical fiber communications has begun.

Understanding fiber optic communications

1. Transmission method: Optical fiber communication is a communication method that uses laser to transmit signals in optical fibers. When using optical fiber to communicate, the laser is injected from one end of the optical fiber, reflected multiple times on the inner wall, and emitted from the other end. The information carried is transmitted to distant places.

Advantages of fiber optic communication:

(1) The transmission frequency band is extremely wide and the communication capacity is large;

(2) Optical fiber has small attenuation, no relay equipment, and long transmission distance;

(3) The frequency is stable and the signal transmission quality is high;

(4) Optical fiber resists electromagnetic interference and has good confidentiality.

3. Note:

(1) Fiber optic communication uses lasers instead of microwaves.

(2) What happens when laser propagates in optical fibers is total reflection, not refraction.

Detection

1. Information theory shows that the higher the _____ of electromagnetic waves as carriers, the more _____ transmitted in the same time.

2. The operating frequency of television broadcasting is generally 30 MHz ~ 3×105MHz, and the operating frequency of sound broadcasting is generally 102 kHz ~ 30MHz. It can be seen that _____ broadcasting transmits more information than _____ broadcasting in the same time.

3. Microwaves are electromagnetic waves with frequencies between ____MHz and ____MHz. The properties of microwaves are closer to ____. They generally propagate along ____. Microwaves ____ (optional "can" or "cannot") orbit along the surface of the earth. Therefore, a ____ must be built every ____km or so to process the incoming signals and then transmit them out to achieve long-distance communication.

4. The development of modern science and technology has enabled people to realize their dream of satellite communications. Satellite communication uses ____ as a relay station for microwave communication.

[Typical example] (2011·Yichang High School Entrance Examination) Regarding optical fiber communication, which of the following statements is wrong?

A. The "wire" used in optical fiber communication is optical fiber

B. The "wires" used in fiber optic communications are metal wires

C. In optical fiber, light propagates forward after multiple reflections.

D. Optical fiber communication can transmit a large amount of information within a certain period of time

[Analysis] Choose B. The "wire" used in optical fiber communication is an optical fiber, not a metal wire. A is correct and B is wrong; the laser is injected from one end of the optical fiber, and after multiple reflections on the inner wall, it is emitted from the other end. , thus transmitting the information it carries to a distant place, C pair; the characteristics of optical fiber communication are small transmission loss and huge communication capacity, D pair.

[Typical example] (2011 Yancheng High School Entrance Examination) In April 2011, our country successfully launched the eighth "Beidou" navigation satellite into space. It used

A. Ultrasonic wave B. Electromagnetic wave

C. Ultraviolet light D. Visible light

[Easy answers] A, C, D

(2011·Guilin High School Entrance Examination) Our city has now fully opened 3G mobile phone communication services. Using 3G mobile phones, you can not only make calls, but also access the Internet through wireless networks at any time. The following statement is correct ( )

A. Electromagnetic waves cannot propagate in vacuum

B. Mobile phone calls directly transmit acoustic signals

C. The propagation speed of electromagnetic waves in the air is 340 m/s

D. Mobile phone wireless Internet access uses electromagnetic waves to transmit digital signals

[Analysis] Choose D. This question examines the transmission of electromagnetic waves and information. Electromagnetic waves can propagate in a vacuum, A is wrong; mobile phone calls use electromagnetic waves to transmit information, B is wrong; the propagation speed of electromagnetic waves in the air is 3×108 m/s , C is wrong; wireless Internet access on mobile phones uses electromagnetic waves to transmit digital signals, D is correct.

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Update Time: 2024-09-30

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